A 16-year-old boy presented with acute lumbar pain and headache, and was hospitalised at a paediatric hospital. The symptoms appeared three days before his admission, the lumbar pain was strong and movement exacerbated it. On admission the patient had nuchal rigidity, bilaterally positive Kernig’s sign and pain of the L4–S1 spinous processes. Blood tests revealed leukocytosis and positive IgM and negative IgG antibodies against Borrelia spp. Cerebrospinal fluid was xanthochromic with a high cell count. Culture of cerebrospinal fluid was negative. Magnetic resonance imaging of the lumbar spine revealed an oval tumour at the level of the L3 vertebra. The tumour was excised completely. Histopathological examination revealed myxopapillary ependymoma of the filum terminale. Conclusion: A sudden and unexplained pain of the lumbar spine appearing in children is an indication for in-depth diagnostic investigation, involving in particular magnetic resonance imaging, which allows one to visualise many pathologies, including spinal canal tumours.